The following description relates generally to an apparatus for transmitting and receiving sound.
Typically, a microphone is a kind of sensors for detecting sound wave or vibration of ultrasonic wave and converting the sound wave or the vibration to an electric signal as an output. Microphones are used as a sound input apparatus in, for example, a recorder, a telephone, a loudspeaker and a hearing device.
Omni-directional microphones have one sound entry opening and ideally accept sound from all directions equally to be susceptible to noise, and for that reason, directional microphones are frequently used to accentuate a useful acoustic signal in an environment filled with interference noise.
FIGS. 1a and 1b illustrate a schematic constitutional view of a conventional omni-directional microphone and a sensitivity characteristic representation in response to sound input direction.
The omni-directional microphone is held adjacent mouth of the user from which sound comes out in order to arrange the microphone nearest to the sound source when the microphone is used in a voice recorder or an car-set for sound detection.
However, as illustrated in FIG. 2, an ear-hole (completely-in-the-canal) sound transmitter/receiver (10) has been developed that receives sound by detecting sound variations generated from a hole (21) of an ear (20) through vibration of ear drum during speaking instead of sound from a mouth. The ear-hole sound transmitter/receiver (10) has an advantage in that it is physically small in size, small enough to fit into a completely-in-the-canal (CIC) hearing aid and it can minimize environmental noise.
There is a disadvantage however in the ear-hole sound transmitter/receiver in that, as input and output of sound are simultaneously realized in the ear holes, sound output of the receiver may be re-inputted into the microphone to become the causes of echo and howling when the omni-directional microphone is employed. Worse yet, a need exists for additional complex signal process for eliminating or attenuating the echo and howling, thereby increasing the sizes and the manufacturing/development costs of the ear-hole sound transmitter/receiver.